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Objective To determine the nanohardness and elastic moduli of two bulk-fill resin based composites (RBCs) at increasing depths from the surface and increasing distances laterally from the center after light curing. Methods Two bulk-fill dental RBCs: Tetric EvoCeram Bulk Fill (TECBF) and Filtek Bulk Fill Flowable (FBFF) were light cured in a metal mold with a 6 mm diameter and a 10 mm long semi-circular notch. The RBCs were photo-polymerized for 10 s using a light emitting diode (LED) Bluephase Style curing light, with the original light probe that lacked the homogenizer. This light has two blue light and one violet light LED emitters. By changing the probe orientation over the mold, the light output from only two LEDs reached the RBC. Measurements were made using: (i) the light from one violet and one blue LED, and (ii) the light from the two blue LEDs. Five specimens of each RBC were made using each LED orientation (total 20 specimens). Specimens were then stored in the dark at 37 °C for 24 h. Fifty indents were made using an Agilent G200 nanoindentor down to 4 mm from the surface and 2.5 mm right and left of the centerline. The results were analyzed ( alpha = 0.05) using multiple paired-sample t -tests, ANOVA, Bonferroni post-hoc tests, and Pearson correlations. Results The elastic modulus and nanohardness varied according to the depth and the distance from the centerline. For TECBF, no significant difference was found between the spatial variations in the elastic modulus or hardness values when violet-blue or blue-blue LEDs were used. For FBFF, the elastic modulus and nanohardness on the side exposed to the violet emitter were significantly less than the side exposed to the blue emitter. A strong correlation between nanohardness and elastic modulus was found in all groups ( r 2 = 0.9512–0.9712). Significance Resin polymerization was not uniform throughout the RBC. The nanohardness and elastic modulus across two RBC materials were found to decline differently according to the orientation of the violet and blue light LED emitters within the curing light. [ABSTRACT FROM AUTHOR]

• A method is described that allows direct comparisons between elution from RBC specimens and from RBC-restored teeth prepared with cavities. • A direct comparison was made of elutable substances from an RBC product family. • GC/MS methods have been used to detect and quantify a range of dimethacrylate monomers in the eluent media and the kinetics of elution. • In addition to elutable (co)monomers, substantial amounts of plasticizers and a UV-stabilizer were found. • An overall assessment of the treatment with regard to elutable substances is recommended, considering the restorative material and adhesive. To develop a model for quantitative comparison of elutable substances by direct elution from resin-bonded composite (RBC) test specimens versus indirect elutability of substances from RBC-restored teeth. Furthermore, it was to be investigated whether the different composites of the Tetric® RBC product family release different types and amounts of substances. Four different composite materials from the Tetric® product family were studied. For each material subgroup ten human third molar teeth were prepared with standard Class-I occlusal cavities. These 'tooth group' specimens were provided with a three-step adhesive system (incorporating TEGDMA) and the respective composite restoration. Same sized control specimens, of each RBC restorative material, were prepared ('direct RBC' groups). All specimens were placed in individual elution chambers such that the elution media (ethanol/water, 3:1) only came into contact with either the tooth root or ¾ height of the 'direct RBC' materials. They were incubated at 37 °C for up to 7 d. Samples of the eluant were taken after 1, 2, 4 and 7 d and were analysed by high-temperature gas chromatography/mass spectrometry. Bisphenol A ethoxylate dimethacrylate (bisEMA), bisphenol A glycidyldimethacrylate (bisGMA), tetraethylene glycol dimethacrylate (TEEGDMA), decan-1,10-diol dimethacrylate (DDDMA) were mostly found in the eluates of the 'direct RBC' groups in statistically significantly greater amounts than in the eluates of the 'tooth groups'. Such quantitative differences were also the case with eluates containing bisphenol A (BPA), dicyclohexyl phthalate (DCHP) and drometrizole, which are common in the environment. In contrast to the behavior found with all the other monomers, up to 3 orders of magnitude more triethylene glycol dimethacrylate (TEGDMA) was found in the 'tooth groups' compared to the 'direct RBC' groups, evidently released by the adhesive system. The release of most of the substances was clearly delayed in the 'tooth groups' indicative of their chronic, rather than acute, elution to the oral environment. A barrier function of the residual dentin layer and the adhesion layer can be inferred. The different release patterns of substances from the various composites of the RBC product family is a manifestation of their different and indication-specific compositions. Consideration of an overall restorative care (RBC plus adhesive) system, when assessing the total amount of released substances, is emphasized. [ABSTRACT FROM AUTHOR]

Objectives To study the effect of resin matrix and maturation time (1 and 24 h) on the creep deformation of resin-composites, two of which have matrix-forming monomers that are either bis-GMA free or have an ormocer structure between the C C groups. Methods Five resin-composites: four commercial and one experimental were investigated. Six specimens were prepared for each material and were divided into two groups ( n = 3) according to the maturation time and condition. Group A was stored dry at room temperature for 1 h and Group B was stored for 24 h in distilled water to allow post-curing at 37 °C. Each specimen was loaded (20 MPa) for 2 h and unloaded for 2 h. The strain deformation was recorded continuously for 4 h. Statistical analysis was performed using one-way ANOVA and the Bonferroni post hoc test at a significance level of a = 0.05. Results The maximum creep-strain % after 1 h ranged from 1.32% to 2.50% and was reduced after 24 h post-cure to between 0.66% and 1.47%. Also, the permanent set after 1 h ranged from 0.70% up to 1.27% (Group A) and after 24 h ranged from 0.53% up to 1.20% (Group B). Significance Creep deformation and maximum recovery for all resin-composites decreased with time, demonstrating improvement in viscoelastic stability. However, there was no significant difference between the permanent set at different times, except for Herculite XRV Ultra. Composites with novel matrices showed comparable properties to existing bis-GMA based materials. [ABSTRACT FROM AUTHOR]

Objective: To study the effect of compositional variables and temperature (25°C and 37°C) on the rheological properties of contemporary resin composites. Methods: Fourteen commercial resin composites with different resin matrices of Bis-GMA and TEGDMA, different filler loading (41–65, v/v) and particle sizes (ranging 5nm to 20μm) were studied using a parallel plate rheometer. Shear sweep measurements were made to determine each composite's viscosity over the angular frequency range of ω =10−4–102 rad/s. Data were analyzed using one way ANOVA, Bonferroni post hoc and t-independent tests (p <0.05). Results: All composites exhibited viscosity reducing with shear rate (pseudoplasticity). Viscosity averages were calculated over the shear rate range. These viscosities increased as the percentage of filler loading (by volume) increased ranging between 0.05–349.33kPas at 25°C and 0.03–132.00kPas at 37°C. Filtek Supreme XTE exhibited the highest viscosity at both temperatures (p <0.05). Filtek Bulk Fill on the other hand, showed the lowest viscosity at both temperatures (p <0.05). Viscosity significantly decreased with the increase in the temperatures for all materials (p <0.05). The reduction ranged from 40.8% (for Venus Diamond Flow) to 92.2% (for Spectrum TPH3). Significances: There was a considerable variation in the resin composite viscosities measured at 25°C as an average value for shear-rate sweep. The factor between the least and highest viscosities was about 7000. The formulation differences that led to such a great variation were primarily: (i) volume fraction of fillers and (ii) particle size, the latter influencing total particle surface area. Rheological properties such as viscosity are key parameters influencing perceived differences in handling behavior of resin composites. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To evaluate the stickiness of unset resin-composites, at different speeds and temperatures, in terms of maximum probe separation-force (F max) and work-of-separation (W s). Materials and methods: Eight commercial light-cured resin-composites were selected. Each material was placed in a cylindrical mold (φ =7mm×5mm depth) held at 25°C or 37°C. The maximum force (F max, N) and work probe separation (W s, Nmm) were measured by using a texture analyzer to register force/displacement. A flat-ended stainless-steel probe (φ =6mm) was mechanically lowered onto and into the surface of the unset sample. When a ‘trigger’ compressive force of 0.05N was registered, data-acquisition commenced. Descent continued until a compressive force of 1N was reached, which was held constant for 1s. Then the probe was moved vertically upward at constant speed. This was varied over the range 2, 4, 6 and 8mm/s. The tensile force produced on the probe by the sticky resin-composite was plotted against displacement and the maximum value was identified (F max). W s was obtained as the integrated area. Data was analyzed by multivariate ANOVA and multiple pair wise comparisons was done by using a Tukey post hoc test to establish homogenous subsets (at p =0.05). Results: F max and W s were taken as potential measures of stickiness. They ranged from 0.47 to 3.68N and from 0.11 to 2.84Nmm, respectively. Multivariate ANOVA showed a strong interaction of withdrawal speed, temperature and materials on both F max and W s (p <0.001). Conclusion: F max and W s are useful parameters for characterizing the handling-stickiness of resin-composite materials, additional to previously reported stickiness-strain or ‘peak-height’. The resin-composites investigated could be differentiated, mostly showing increases in F max and W s stickiness with increased temperature and probe-withdrawal speed. [Copyright &y& Elsevier]

Abstract: Objectives: Stickiness is a vital rheological parameter for the clinical handling behavior of unset resin composite restoratives. The aim of this study was to investigate the stickiness of three different resin composites at 23°C and 37°C tested on steel, dentin and dentin covered with different bonding agents. Methods: The stickiness instrument, used in this study consists of a vertical cylindrical stainless steel rod, with a flat circular end, and a platform with a cylindrical mold (diameter: 6.1mm, depth: 2.2mm). The test-material surface temperature and the speed of the rod can be modified. It moves slowly into the prepared mold which is filled with unset composite materials. The degree of stickiness is deducted from the height of the “elevation” the material forms when the plunger is withdrawn from the mold until the steelhead detaches itself from the composite. In this study, stickiness was tested directly to the steel plunger and to dentin slices (uncovered or covered with two different bonding agents) fixed to the plunger rod with a clamp. Results: The coefficients of variation (CVs) were generally less than 0.10, indicating that the stickiness instrument offers an adequately reproducible way of testing stickiness. The tested composite materials varied significantly in stickiness. For all investigated materials a decrease of peak heights with increasing speed was found (for all three materials: p <0.0001). Generally the stickiness increased when increasing the temperature from 23°C to 37°C. Comparing the areas under the curve (), stickiness of resin composites was higher on dentin than on steel and least on bonded dentin. The order of stickiness of composites was not affected by testing the stickiness on the different materials. Significance: This method allows the characterization of composite resin materials stickiness to steel, as equivalent to dental steel instruments, and to bonded dentin as equivalent to the tooth cavity after preparation. An ideal material should have a sufficient difference between stickiness on steel and dentin so that it remains in the cavity and is not pulled back by the steel instrument. [Copyright &y& Elsevier]

To investigate the influence of different resin composite and glass ionomer cement material combinations in a "bi-layer" versus a "single-layer" adhesive technique for class I cavity restorations in molars using numerical finite element analysis (FEA). Three virtual restored lower molar models with class I cavities 4 mm deep were created from a sound molar CAD model. A combination of an adhesive and flowable composite with bulk fill composite (model A), of a glass ionomer cement with bulk fill composite (model B) and of an adhesive with bulk fill composite (model C), were considered. Starting from CAD models, 3D-finite element (FE) models were created and analyzed. Solid food was modeled on the occlusal surface and slide-type contact elements were used between tooth surface and food. Polymerization shrinkage was simulated for the composite materials. Physiological masticatory loads were applied to these systems combined with shrinkage. Static linear analyses were carried out. The maximum normal stress criterion was adopted as a measure of potential damage. All models exhibited high stresses principally located along the tooth tissues–restoration interfaces. All models showed a similar stress trend along enamel–restoration interface, where stresses up to 22 MPa and 19 MPa was recorded in the enamel and restoration, respectively. A and C models showed a similar stress trend along the dentin-restoration interface with a lower stress level in model A, where stresses up to 11.5 MPa and 7.5 MPa were recorded in the dentin and restoration, respectively, whereas stresses of 17 MPa and 9 MPa were detected for model C. In contrast to A and C models, the model B showed a reduced stress level in dentin, in the lower restoration layer and no stress on the cavity floor. FE analysis supported the positive effect of a "bi-layer" restorative technique in a 4 mm deep class I cavities in lower molars versus "single-layer" bulk fill composite technique. [ABSTRACT FROM AUTHOR]

Objectives To assess conceptual designs of dental posts consisting of polyetherimide (PEI) reinforced with carbon (C) and glass (G) glass fibers in endodontically treated anterior teeth. Methods 3D tessellated CAD and geometric models of endodontically treated anterior teeth were generated from Micro-CT scan images. Model C-G/PEI composite posts with different Young’s moduli were analyzed by Finite Element (FE) methods post A (57.7 GPa), post B (31.6 GPa), post C (from 57.7 to 9.0 GPa in the coronal–apical direction). A load of 50 N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum principal stress distribution was determined along the post and at the interface between the post and the surrounding structure. Results Post C, with Young’s modulus decreasing from 57.7 to 9.0 GPa in the coronal–apical direction, reduced the maximum principal stress distribution in the restored tooth. Post C gave reduced stress and the most uniform stress distribution with no stress concentration, compared to the other C-G/PEI composite posts. Significance The FE analysis confirmed the ability of the functionally graded post to dissipate stress from the coronal to the apical end. Hence actual (physical) C-G/PEI posts could permit optimization of stress distributions in endodontically treated anterior teeth. [ABSTRACT FROM AUTHOR]

Objectives To investigate the influence of specific resin-composite, glass ceramic and glass ionomer cement (GIC) material combinations in a “multi-layer” technique to replace enamel and dentin in class II mesio-occlusal-distal (MOD) dental restorations using 3D-Finite Element Analysis (FEA). Methods Four 3D-FE models (A–D) of teeth, adhesively restored with different filling materials, were created and analyzed in comparison with a 3D model (E) of a sound lower molar. Models A, B & C had “multilayer” constructions, consisting of three layers: adhesive, dentin replacement and enamel replacement. Model A : had a low modulus (8 GPa) composite replacing dentin and a higher modulus (12 GPa) composite replacing enamel. Model B: had a GI cement replacing dentin and a higher modulus (12 GPa) composite replacing enamel. Model C : had a low modulus (8 GPa) composite replacing dentin and a very high modulus (70 GPa) inlay replacing enamel. Model D : had a lithium disilicate inlay replacing both dentin and enamel with a luting cement base-layer. Polymerization shrinkage effects were simulated and a load of 600 N was applied. All the materials were assumed to behave elastically throughout the entire deformation. Results Model A showed the highest stress distribution along all the adhesive interfaces of the shrinking resin-based materials with a critical condition and failure risk marginally and internally. Model D, by contrast, showed a more favorable performance than either of the multilayer groups (A–C). Stress and displacement plots showed an elastic response similar to that obtained for the sound tooth model. Model B and Model C performed according to their bilayer material properties. The use of a non-shrink dentin component simulating a GIC clearly affected the shrinkage stress at the basis of the Model B; while the bulk resin composite having a 12 GPa Young’s modulus and linear polymerization shrinkage of 1% strongly influenced the biomechanical response in the bucco-lingual direction. Significance Direct resin-based composite materials applied in multilayer techniques to large class II cavities, with or without shrinking dentin layers, produced adverse FEA stress distributions and displacements. An indirect lithium disilicate inlay used to replace lost dentin and enamel in posterior restored teeth generated lower stress levels, within the limits of the elastic FEA model. [ABSTRACT FROM AUTHOR]

Objectives To study the influence of resin based and lithium disilicate materials on the stress and strain distributions in adhesive class II mesio-occlusal-distal (MOD) restorations using numerical finite element analysis (FEA). To investigate the materials combinations in the restored teeth during mastication and their ability to relieve stresses. Methods One 3D model of a sound lower molar and three 3D class II MOD cavity models with 95° cavity-margin-angle shapes were modelled. Different material combinations were simulated: model A, with a 10 μm thick resin bonding layer and a resin composite bulk filling material; model B, with a 70 μm resin cement with an indirect CAD-CAM resin composite inlay; model C, with a 70 μm thick resin cement with an indirect lithium disilicate machinable inlay. To simulate polymerization shrinkage effects in the adhesive layers and bulk fill composite, the thermal expansion approach was used. Shell elements were employed for representing the adhesive layers. 3D solid CTETRA elements with four grid points were employed for modelling the food bolus and tooth. Slide-type contact elements were used between the tooth surface and food. A vertical occlusal load of 600 N was applied, and nodal displacements on the bottom cutting surfaces were constrained in all directions. All the materials were assumed to be isotropic and elastic and a static linear analysis was performed. Results Displacements were different in models A, B and C. Polymerization shrinkage hardly affected model A and mastication only partially affected mechanical behavior. Shrinkage stress peaks were mainly located marginally along the enamel-restoration interface at occlusal and mesio-distal sites. However, at the internal dentinal walls, stress distributions were critical with the highest maximum stresses concentrated in the proximal boxes. In models B and C, shrinkage stress was only produced by the 70 μm thick resin layer, but the magnitudes depended on the Young’s modulus (E) of the inlay materials. Model B mastication behavior (with E = 20 GPa) was similar to the sound tooth stress relief pattern. Model B internally showed differences from the sound tooth model but reduced maximum stresses than model A and partially than model C. Model C (with E = 70 GPa) behaved similarly to model B with well redistributed stresses at the occlusal margins and the lateral sides with higher stress concentrations in the proximal boxes. Models B and C showed a more favorable performance than model A with elastic biomechanics similar to the sound tooth model. Significance Bulk filling resin composite with 1% linear polymerization shrinkage negatively affected the mechanical behavior of class II MOD restored teeth. Class II MOD direct resin composite showed greater potential for damage because of higher internal and marginal stress evolution during resin polymerization shrinkage. With a large class II MOD cavity an indirect composite or a lithium disilicate inlay restoration may provide a mechanical response close to that of a sound tooth. [ABSTRACT FROM AUTHOR]

Objectives To investigate the sorption, solubility, mass change and hygroscopic expansion (solvent swelling) of resin-composites after long term storage in different solvents. Methods Eight materials were studied: two bulk-fill flowable materials (SDR and Venus bulk fill, V-BF), a packable bulk-fill material (Tetric Evoceram bulk-fill, TET-BF), a fiber reinforced material (Ever X posterior, EVX), a nano-hybrid conventional material (Tetric Evoceram, TET) and micro-hybrid conventional materials (G-aenial anterior, GA-P and posterior, GA-A). Three groups of disk shaped specimens were prepared using split stainless steel molds. Each group was stored, respectively, in: water, 75% ethanol/water and methyl ethyl ketone (MEK). The total storage time was 180 d plus a reconditioning time of 120 d. A non-contact laser scanning micrometer was used to measure the diametral changes. Results Significant differences were found in the sorption and solubility of the materials. Generally, MEK stored specimens had the highest values followed by 75% ethanol/water then water. A similar trend was found with the mass and volume changes (except for EVX). V-BF showed the highest sorption (98.1 μg/mm 3 ) and solubility (10 μg/mm 3 ) after MEK storage. Mass and volume changes showed near-linear correlation, with high Pearson coefficients (0.86–0.99). Significance Generally the materials were most greatly affected by MEK storage compared to the other two solvents. The glass-fiber-reinforced EVX, however, was most affected by water immersion. The pattern of change/recovery behavior of the materials, during solvent challenge, was similar to the pattern of viscoelastic creep/recovery behavior of resin-composite materials. [ABSTRACT FROM AUTHOR]

Objective Since bulk-fill (BF) resin composites should cure efficiently to a depth up to 4 mm, the aim of the study was to determine the time-dependence of degree of conversion (DC) at that depth during 24 h post-irradiation. Methods Eight representative BF resin composites were studied [x-tra base (XTB), Venus Bulk Fill (VBF), Tetric EvoCeram Bulk Fill (TECBF), Sonic Fill (SF), Filtek Bulk Fill (FBF), everX Posterior (eXP), Beautifil-Bulk Flowable (BBF), Beautifil-Bulk Restorative (BBR)]. Specimens were fabricated in white Delrin moulds of 4 mm height and 5 mm internal diameter directly on an attenuated total reflectance (ATR) accessory attachment of an (FTIR) spectrometer (Nicolet iS50, Thermo Fisher, Madison, USA). Upper specimen surfaces were irradiated in situ for 20 s with an LED curing unit (Elipar S10 with average tip irradiance of 1200 mW/cm 2 ). Spectra from the lower surface were recorded continuously in real-time for 5 min and then at 30 and 60 min and 24 h post irradiation. Results Mean ranges of DC 4mm (%) of the materials at 4 mm depth were 39–67; 48–75; 45–74; and 50–72 at 5, 30 and 60 min and 24 h respectively. DCs for XTB, VBF, TECBF, FBF, BBR increased significantly 30 min after irradiation ( p < 0.05) and were not affected by subsequent time up to 24 h ( p > 0.05). DC for SF was not affected by subsequent time after 5 min ( p > 0.05). For eXP and BBF, DC increased 24 h after irradiation ( p < 0.05). The data were described by the superposition of two exponential functions characterising the gel phase (described by parameters a, b) and the glass phase (described by parameters c and d). Significance Post polymerization impact of bulk-fill composites is material dependent. Five materials exhibited their maximum DC 4mm already 30 min after starting the irradiation while DC 4mm for two materials optimized after 24 h. BF materials were found to exhibit after 24 h a DC between 50 and 72% at 4 mm depth under the stated irradiation conditions. [ABSTRACT FROM AUTHOR]

Objectives In the revised version of ISO 7405 there are so far no detailed recommendations concerning temperature and humidity during specimen production for light curing and chemically setting dental materials. The main objective of the present study was to observe if different environmental conditions during specimen production influence cytotoxicity and degree of conversion of four post and core composite materials and to investigate if cytotoxicity of post and core materials is influenced by their corresponding bonding substances. Methods Specimens of four different post and core composite materials (LuxaCore – Dual, Core X-Flow, Flow White and MultiCore Flow) were produced in a climate test chamber at 23 °C/50% relative humidity or 37 °C/95% relative humidity and were dual-cured or self-cured, with or without their corresponding bonding substances. Specimens were added to cell cultures immediately after production or after preincubation for 7 days. Specimens were incubated with L-929 fibroblasts for 72 h and cell numbers determined by a flow cytometer. FTIR spectroscopic measurements of post and core materials were performed at the same temperature conditions as for the cytotoxicity assay (23 °C or 37 °C). Results Dual-cured specimens of all post and core composites exhibited less cytotoxicity under both environmental conditions than self-cured specimens. All self-cured specimens manufactured at 37 °C/95% showed less cytotoxicity than specimens produced at 23 °C/50%. All dual-cured specimens showed similar cytotoxicity at both environmental conditions. After 7 days of preincubation most dual-cured specimens produced at 23 °C/50% showed less cytotoxicity than self-cured specimens (with the exception of Flow White). Compared to fresh specimens, 7-day aged specimens of most materials showed reduced cytotoxicity. Materials already showing low cytotoxicity as fresh specimens did not further reduce their cytotoxicity after 7 days of preincubation. For dual-cured materials the degree of conversion was higher compared to self-cured materials. Significance Different temperatures during specimen production have an impact on cytotoxicity and degree of conversion of dual-curing composite materials. Detailed recommendations for standardization concerning environmental conditions during specimen production are required. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The aim of this study was to numerically evaluate the effects of filler contents and resin properties on the material properties of dental composites utilizing realistic 3D micromechanical finite element models. Methods: 3D micromechanical finite element models of dental composites containing irregular fillers with non-uniform sizes were created based on a large-scale, surrogate mixture fabricated from irregularly shaped stones and casting resin. The surrogate mixture was first scanned with a micro-CT scanner, and the images reassembled to produce a 3D finite element model. Different filler fractions were achieved by adjusting the matrix volume while keeping the fillers unchanged. Polymerization shrinkage, Young''s modulus, Poisson''s ratio and viscosity of the model composites were predicted using the finite element models, and their dependence on the filler fraction and material properties of the resin matrix were considered. Comparison of the numerical predictions with available experimental data and analytical models from the literature was performed. Results: Increased filler fraction resulted in lower material shrinkage, higher Young''s modulus, lower Poisson''s ratio and higher viscosity in the composite. Predicted shrinkage and Young''s modulus agreed well with the experimental data and analytical predictions. The McGee–McCullough model best fit the shrinkage and Young''s modulus predicted by the finite element method. However, a new parameter, used as the exponent of the filler fraction, had to be introduced to the McGee–McCullough model to better match the predicted viscosity and Poisson''s ratio with those from the finite element analysis. Significance: Realistic micro-structural finite element models were successfully applied to study the effects of filler fraction and matrix properties on a wide range of mechanical properties of dental composites with irregular fillers. The results can be used to direct the design of such materials to achieve the desired mechanical properties. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of this study was to investigate the effect of variations in filler particle size and shape on the polymerization shrinkage-stress kinetics of resin-composites. Methods: A model series of 12 VLC resin-composites were studied. The particulate dispersed phase volume fraction was 56.7%: these filler particles were systematically graded in size, and further were either spherical or irregular. A Bioman instrument (cantilever beam method) was employed to determine the shrinkage-stress kinetics following 40s irradiation (600mW/cm2) at 23°C (n =3). All data were captured for 60min and the final shrinkage-stress calculated. Results: Shrinkage-stress varied between 3.86MPa (SD 0.14) for S3 (spherical filler particles of 500nm) and 8.44MPa (SD 0.41) for I1 (irregular filler particles of 450nm). The shrinkage-stress values were generally lower for those composites with spherical filler particles than those with irregular filler particles. The differences in shrinkage-stress with filler particle size and shape were statistically significant (p <0.001). Significance: Composites with spherical filler particles exhibit lower shrinkage-stress values compared to those with irregular filler particles. Shrinkage-stress and shrinkage-stress rate vary in a complex manner with variations in the size of the dispersed phase particles: a hypothesized explanation for the effect of filler particle size and shape is presented. [Copyright &y& Elsevier]

Abstract: Objectives: The study was aimed at investigating the cytotoxicity of different composites as a function of composite shade and the light curing unit (LCU) employed. Methods: Non-polymerized and polymerized samples of the composites Grandio® (VOCO, Cuxhaven), Solitaire® (Heraeus Kulzer, Hanau) and Filtek Z 250® (3M/Espe, Seefeld) in two markedly differing shades (A2, C2) were prepared. Polymerization was performed with two LCUs: Heliolux II (Ivoclar/Vivadent, Ellwangen) and Swiss Master Light (EMS, Nyon, Switzerland). To obtain composite extracts, the samples were immersed in cell culture medium (DMEM – Dulbecco‘s Modified Eagle Medium), which was replaced daily up to the 7th day of the experiment, and then on the 14th, 21st and 28th day. After incubation of human gingival fibroblasts (HGF) with the extracts obtained, cytotoxicity was determined using the MTT test. Results: With the non-polymerized samples, essentially no influence of the composite shades investigated on HGF viability was detected, with the exception of the Solitaire material, where a higher cytotoxicity of the shade C2 in the non-polymerized state was found at the end of the observation period. After polymerization of the different composites, the cytotoxic reaction observed for the extracts of shade C2 was stronger than that observed for A2. After polymerization with the Heliolux II (HLX) LCU, the extracts of composites Grandio and Solitaire C2 were significantly more toxic than those of the A2 shade (p <0.01). Polymerization with the Swiss Master Light (SML) reduces this cytotoxic effect. The extracts of the Grandio composite showed the least cytotoxic effect throughout the observation period, irrespective of the LCU used. For the extracts of the Z250 specimens, the cytotoxicity observed was generally higher. Significance: The results show that the shade of the composite has an influence on its cytotoxicity and that this cytotoxicity is also influenced by the light curing unit used. It was observed that composites of the darker shade (C2) had a higher cytotoxicity, which varied with the LCU employed. [Copyright &y& Elsevier]

Abstract: Objectives: To investigate the influence of matrix and filler content on degradation resistance of an experimental pure-ormocer and an dimethacrylate-based composite derived from a commercially available material. Materials and methods: A dimethacrylate- Grandio (GR) and a model pure ormocer-based-matrix ORMOCER (ORM) were used. Each material had three different types according to their filler content (% w/w): regular (87% and 86%), flowable (80% and 79%) and fissure sealer (70% and 69%) for GR and ORM respectively. Disc-shaped (1mm thickness×10mm diameter) samples were prepared for each material (n =6). Water sorption and solubility tests were adapted from ISO4049. To evaluate porosity, specimens were scanned at a resolution of 19.4μm and 3D reconstructions were made. The volume ratio of pores in the specimens were calculated and expressed as percentages. The results were submitted to 2-way ANOVA (factors: matrix and filler content) and Tukey post-hoc statistic test (p =0.05). Results: Filler content influenced the water sorption for the ormocer-matrix and the water solubility for the dimethacrylates. ORMOCER regular was a less porous material compared to flowable and sealer formulations. On the other hand, the filler content had no effect on porosity for Grandio. Conclusion: Modifications made in the pure ormocer-matrix formulation were not significantly important to produce a more water-stable material compared to the dimethacrylate-matrix composite materials. [Copyright &y& Elsevier]

Abstract: Objectives: To investigate the kinetic process of water diffusion and mass change in new resin–matrix composites during water sorption/desorption cycles. Methods: Five new resin–matrix composites were investigated [Filtek® Silorane (FS), GC Gradia Direct Anterior (GDA), GC Gradia Direct Posterior (GDP), GC Kalore (GCK), Vertise® Flow (VF)]. Five disk-shaped specimens, per material (15.0±0.1)mm diameter by (2.0±0.1)mm, were prepared according to ISO 4049. Each disk was immersed separately in de-ionized water for 150d and then reconditioned for 75d; all at (37±1)°C. Mass was measured at different time intervals. Perspex disks were used as control. Data analysis was done by repeated measures ANOVA, one-way ANOVA and Tukey''s post hoc test (p <0.05). Results: The water sorption (μg/mm3) after 150d immersion ranged from 13.51μg/mm3 (±0.40) for FS to 71.96μg/mm3 (±0.90) for VF. The solubility ranged up to 16.95μg/mm3 (±0.79) for VF. A significant mass reduction occurred in VF after the peak value [73.63μg/mm3 (±0.31)] of water sorption was reached at 42d. VF had the highest diffusion-coefficient for sorption: 5.23×10−9 cm2/s (±0.38) and desorption: 11.72×10−9 cm2/s (±0.16). Percentage sorption differences were significant for all materials (p <0.001), except between GCK and GDP. The early correlation between mass change and square root of time was linear. Significance: Each resin–matrix composite varied in sorption/desorption cycles which may affect clinical service. A concurrent solubility process occurred during sorption of the self-adhering composite VF. The silorane composite FS exhibited minimal sorption. [Copyright &y& Elsevier]

Abstract: Objective: To investigate the surface integrity of solvent-challenged ormocer-matrix composites, photoactivated by different light exposure modes, through surface-hardness measurements at different periods of time; and to compare such behavior with dimethacrylate-based materials. Methods: One hundred percent ormocer-based matrix (experimental ormocer (ORM)), a commercial mixed dimethacrylate-ormocer-based matrix (Admira (ADR)) and two commercial dimethacrylate-based matrix composites (experimental controls, (Grandio (GRD) and Premise (PRE)) were evaluated. Disk specimens (4mm×2mm) were prepared from each material and light-activated using either a standard (S) or soft-start (SS) light exposure protocol with an LED-curing unit. Top, irradiated surface Knoop hardness (KHN) was measured within the following experimental groups (n =5): Group 1: immediately after exposure; Group 2: after dry and dark storage, Group 3: after storage in distilled water, and Group 4: immersion in absolute ethanol. Hardness of Groups 2–4 were measured after 7 days storage. Immediate hardness values were submitted to Student''s t-tests separately for each material. Hardness values after treatments were submitted to two-way ANOVA and Tukey''s post hoc test to compare values among different storage media and light exposure mode protocols. Comparisons among materials were described using percentage of hardness change. Statistical testing was performed at a pre-set alpha of 0.05. Results: Immediate hardness values were not affected by the light exposure mode, regardless of the material. In general, exposure mode did not significantly affect hardness after 7 days storage, regardless of storage media or material. After 7 days dry storage, hardness values increased for all materials relative to immediate testing, and decreased after water and ethanol storage, with ethanol showing the greatest effect. The experimental ormocer-based material had the lowest percentage hardness change and thus proved more resistant to solvent degradation than the other materials, regardless of the light exposure method. Significance: Irradiated surface hardness values and surface integrity were unaffected by light exposure mode, regardless of the material tested. The experimental ormocer-based material presented the least change in hardness as a result of solvent challenge than any of the commercial products: ormocer or conventional resin-based, and thus showed better surface integrity. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of this study was to measure the full-field polymerization shrinkage of dental composites using optical image correlation method. Methods: Bar specimens of cross-section 4mm×2mm and length 10mm approximately were light cured with two irradiances, 450mW/cm2 and 180mW/cm2, respectively. The curing light was generated with Optilux 501 (Kerr) and the two different irradiances were achieved by adjusting the distance between the light tip and the specimen. A single-camera 2D measuring system was used to record the deformation of the composite specimen for 30min at a frequency of 0.1Hz. The specimen surface under observation was sprayed with paint to produce sufficient contrast to allow tracking of individual points on the surface. The curing light was applied to one end of the specimen for 40s during which the painted surface was fully covered. After curing, the cover was removed immediately so that deformation of the painted surface could be recorded by the camera. The images were then analyzed with specialist software and the volumetric shrinkage determined along the beam length. Results: A typical shrinkage strain field obtained on a specimen surface was highly non-uniform, even at positions of constant distance from the irradiation surface, indicating possible heterogeneity in material composition and shrinkage behavior in the composite. The maximum volumetric shrinkage strain of ∼1.5% occurred at a subsurface distance of about 1mm, instead of at the irradiation surface. After reaching its peak value, the shrinkage strain then gradually decreased with increasing distance along the beam length, before leveling off to a value of approximately 0.2% at a distance of 4–5mm. The maximum volumetric shrinkage obtained agreed well with the value of 1.6% reported by the manufacturer for the composite examined in this work. Using irradiance of 180mW/cm2 resulted in only slightly less polymerization shrinkage than using irradiance of 450mW/cm2. Significance: Compared to the other measurement methods, the image correlation method is capable of producing full-field information about the polymerization shrinkage behavior of dental composites. [Copyright &y& Elsevier]